1. Field of the Invention
The present invention relates to a decorative molded object which has a color design image such as a letter, a symbol, or a pattern displayed in color, and is incorporated in a part of various products to exert a display function and a decoration function, and to a method of producing the same. In particular, the present invention relates to a key top for a push-button switch used for input operation portions of various electronic instruments such as mobile telephones, mobile data terminals, and AV equipment.
2. Description of the Related Art
There have been known various decorative molded objects each of which has a color design image such as a letter, a symbol, or a pattern displayed in color, and is incorporated in a part of various products to exert a display function and a decoration function. For instance, a mobile telephone is taken as an example. A key top for a push-button switch used in a mobile telephone is a decorative molded object in which a key top made of resin is provided with a color design image such as a letter or a pattern. A case constituting a mobile telephone itself is also a decorative molded object having a color design image provided that the case has a pattern drawn on its surface.
Each of those decorative molded objects is formed by forming a color design image on a resin surface, followed by molding into a predetermined shape, or is formed by molding a resin into a predetermined shape, followed by printing or applying a color design image. A description will be made by taking a key top for a push-button switch used in an electronic instrument such as a mobile telephone as an example. A display portion, which is provided on the surface of the key top for a push-button switch and is composed of a color design image such as a letter or a pattern, is mainly formed by applying screen printing, pad printing, or the like to a key top main body made of resin.
However, in accordance with recent miniaturization and multi-functionality of electronic instruments, miniaturization of decorative molded objects such as a push-button has been demanded, and there has been a growing need for displaying, in a limited space, a larger number of letters, numeric characters, or symbols, or a figure, a design pattern, or the like which is complicated and composed of multiple colors. However, in the conventional approach such as screen printing or pad printing, a printing plate has been necessary for each color, and a sophisticated printing technique has been necessary for alignment of each color. Therefore, a quick response involved in diversification of a design and shortening of cycles was difficult to be made, so that the needs for simplification of a production step, a cost reduction, and an increase in resolution could not be satisfied.
On the other hand, as a method of forming a display portion alternative to the conventional printing method, there is a method which includes laminating a printing sheet obtained by printing graphics on a resin sheet by means of a printer onto a resin molded object, and JP 2000-231849 A discloses a similar technique. However, the method requires a post-step of cutting the printing sheet along an outer peripheral shape of each key top by using a carbon dioxide laser or a punching blade. In addition, a thick printing sheet is cut, so that there arises a problem in that a burr tends to be produced at a cut surface. Furthermore, the printing sheet is integrated into the key top, which is not suitable regarding a response to a reduction in thickness of the key top for a push-button switch.
JP 2000-231849 A
In view of the above, as a method with which a letter, a pattern, or the like that has been difficult to be displayed at a high resolution with the conventional printing method such as screen printing or pad printing can be clearly displayed at a high resolution, and which responds to a demand for a reduction in thickness that has been difficult in the method of laminating a printing sheet onto a resin molded object, the following method has been attempted. The method includes: printing a color design image representing a letter, a symbol, a figure, or the like on a substrate sheet by means of an output apparatus for collectively outputting color design data such as a printer; and transferring the resultant color design image onto a resin molded object. However, there have been problems in that a bad combination of a color printer and a substrate sheet results in a partial printing running off the letter edge in the printed image, and that, even if a high-quality image is printed, transfer is not performed with satisfaction at the stage of transferring the image onto the resin molded object. Moreover, for example, there has been a problem in that, even if the steps up to the transfer are performed with satisfaction, the obtained color design image becomes yellowish or the like, resulting in poor transparency.
The inventors of the present invention have made extensive studies in order to solve those problems, and have found that, by conducting processing onto a printing surface side of a substrate sheet and processing onto an image surface in combination, a design image can be obtained, which has a high resolution such as fineness of a drawing or smoothness of image quality, and which is clear and excellent in transparency. Thus, the inventors of the present invention have completed the present invention on the basis of this finding.